I use Flash memory on my KD43XD8305 and have found it excellent, however its not all plain sailing...
Sandisk drives have worked for me and you don't appear to need high speed USB3:0 or 3:1 types, the older USB2:0 types seem fine. Sony even state somewhere that there are NO requirements on transfer rate speeds.
I have only used 64Gb capacity, mainly because I have a dedicated HDD recorder (Sony HXD870 with 1Tb drive), however the USB facility is great.
64Gb holds way more than you might think with an hours HD content using a couple of Gb and SD content much less.
Problems can occur (and these are documented by others and also experienced by me) if you come to disconnect or re-use the drive. The TV formats the drive with a unique file system and changes the legacy MBR (Master Boot Record) to GPT (GUID Partition Table). This means the drive will probably not just work again on a PC unless you reconfigure and reformat it. This is easily done with a few simple commands.
